Wednesday, May 27, 2015

Fuel Trims

Ok so we are using this program called Scan XL Pro to try to diagnose what I *think* may be a vacuum leak in our 1998 SLK230 4 banger. I am only *guessing* that it's a vacuum leak because it seems to be sapping our fuel economy and causing a rough idle. From looking at these graphs, you can see that our LTFT (long term fuel trim) starts out at 29% and eventually climbs to 31% which is awfully high. This means the fuel trim is trying to compensate for a lean condition in the engine. Anyhow here are the graphs-

This one is just us sitting in the parking lot revving the engine...

Things start to get a bit complicated when we take it for a spin on the freeway...

Judging from the way the MAP (manifold absolute pressure) is all over the place I want to say that its either something wrong with the MAP sensor, which is causing the fuel trim to tweak out, or a leak in the intake manifold gasket. What do you think???

OK one more graph, this one depicting the TPS (throttle position sensor)

No comments:

Post a Comment